The present technology relates to a solid-state imaging device, a driving method thereof and an electronic apparatus, and, particularly, to a solid-state imaging device which allows transfer capability of an electric charge to be ensured without sacrificing sensitivity and a held electric charge quantity, a driving method thereof and an electronic apparatus.
In the related art, a solid-state imaging device such as a Complementary Metal Oxide Semiconductor (CMOS) image sensor is widely used for a digital still camera, a digital video camera and the like.
Further, as a system of an electronic shutter of the CMOS image sensor, a global shutter system is proposed (see Japanese Unexamined patent Application Publication No. 2012-129797 and Japanese Unexamined patent Application Publication No. 2011-217315). The global shutter system performs operation that starts exposure for all pixels effective for imaging at the same time and completes the exposure at the same time. Thus, equipping of a memory section for temporarily holding an optical electric charge accumulated by a photodiode while waiting for order of reading after the exposure is completed is necessary.
That is, as illustrated in a cross-sectional view of unit pixel of FIG. 1, a pixel structure is used in which a pixel structure is used in which a memory section (MEM) 23 is provided inside the unit pixel and electric charge accumulated in a photodiode (PD) 21 is transferred concurrently for all pixels to the memory section 23 by a first transfer gate (TRX) 22, and the electric charge is held until a reading operation is performed for each row.
Here, a driving method of the unit pixel of FIG. 1 is described with reference to FIGS. 2 and 3. However, in a potential diagram of FIG. 3, states of a period t1 to period t5 correspond respectively to a period t1 to a period t5 in a timing chart of FIG. 2.
In the period t1, if the electric charge of the photodiode 21 and the memory section 23 is discharged, the electric charge obtained from light from an object is newly accumulated in the photodiode 21 concurrently for all pixels. Further, in the period t2, if a voltage level of a drive signal applied to a gate electrode of the first transfer gate 22 becomes a VH level, the electric charge accumulated in the photodiode 21 is transferred to the memory section 23. Then, in the period t3, if the voltage level of the drive signal applied to the gate electrode of the first transfer gate 22 becomes a VL level, the electric charge is held in the memory section 23.
Thereafter, in the period t4, the voltage level of the drive signal applied to a gate electrode of a second transfer gate (TRG) 24 becomes the VH level, and the electric charge held in the memory section 23 is transferred to a Floating Diffusion (FD) region 25. Then, in the period t5, if the voltage level of the drive signal applied to the gate electrode of the second transfer gate 24 becomes the VL level, a voltage corresponding to the electric charge held in the floating diffusion region 25 is read as a signal level.